A surprising public health policy in Wales may have revealed powerful evidence that the shingles vaccine could help reduce the risk of developing dementia.
In a new study led by Stanford Medicine and published in the journal Nature, researchers discovered that older adults who received the shingles vaccine were 20% less likely to develop dementia over the next seven years compared to those who didn’t get the vaccine.
Shingles is caused by the varicella-zoster virus, the same virus responsible for chickenpox. After someone recovers from chickenpox, the virus remains dormant in their body and can reactivate later in life as shingles, especially in older adults. Some scientists believe viruses like this that affect the nervous system may increase the risk of dementia.
Past studies hinted at a connection between shingles vaccination and reduced dementia risk. However, those studies couldn’t rule out other factors, such as the general health-consciousness of people who choose to get vaccinated.
People who are more likely to get vaccines often eat better, exercise more, and go to the doctor more regularly, all of which may also lower the risk of dementia.
But the rollout of the shingles vaccine in Wales gave researchers a unique chance to study this connection in a near-randomized way.
Beginning in 2013, Wales offered the vaccine only to people who were 79 years old as of September 1 that year. Those who were even a few days older were not eligible and would never be offered the vaccine due to limited supply.
This one-year age cutoff created two very similar groups—those eligible and those not—who differed only in their ability to receive the vaccine. By comparing these groups, researchers were able to isolate the effect of the vaccine itself.
The study looked at health records from over 280,000 adults aged 71 to 88. Among those who turned 80 just before the cutoff and just after, researchers found that people who received the vaccine had a 20% lower risk of developing dementia. The vaccine also reduced the risk of shingles by 37%, similar to previous clinical trial results.
The protective effect was especially strong in women, possibly due to differences in immune response or the way dementia develops across sexes. Women tend to have stronger immune responses to vaccines and are also more likely to develop shingles.
Researchers believe the vaccine may help protect against dementia either by boosting the immune system in general or by preventing reactivations of the virus. However, the exact mechanism remains unclear.
While the older, live-attenuated shingles vaccine is no longer manufactured, a newer version that uses only parts of the virus is more effective at preventing shingles. It’s unknown whether this newer version has similar or better effects on dementia.
The researchers have since found similar results in health records from other countries like England, Australia, and Canada. They are now pushing for a randomized controlled trial—the gold standard for proving cause and effect.
Dr. Pascal Geldsetzer, the study’s lead author, said such a trial could provide the evidence needed to make the shingles vaccine part of dementia prevention strategies.
The study is published in Nature.
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